I'm quite large (30g) and can't be without underwires, I have not found a non underwired bra that actually supports me. But I live in a hot place so I have to have my boobs separate. I absolutly would hate them to be touching the skin underneath on my body, or touching each other. I really need support or I would sweat in summer. So after trying on loads of nursing bras, and finding out I'm a 30 not 32 so virtually no nursing bras are even made in my band size let along cup size (I think there are about 3 or 4 options for me) I gave in. I bought normal bras that I liked, and bought the nursing clips separatly to convert a bra to a nursing bra. If you do end up struggling to find a bra that fits, or find a good bra reduced (is it just me or are nursing bras really expensive) then bear in mind you can buy the clips to convert a normal bra for hardly any money.
Also don't listen to 'people' who say you can buy your bras at 36 weeks, buy a nursing bra when the baby is a weekor two old. Your boobs can really change in those first few weeks.